Water-based ink set for ink-jet recording and ink-jet recording method

ABSTRACT

A water-based ink set for ink-jet recording is provided which is capable of: reducing graininess in a low-density printed part without reducing the color reproduction range in red and magenta directions in a high-density printed part; extending the color reproduction range in the red direction; improving the vividness of the red color; and improving the light fastness and gas resistance. The water-based ink set for ink-jet recording includes a magenta pigment ink and a red dye ink. The magenta pigment ink is a light magenta pigment ink having a lightness (L*) of about 50 or more in the L*a*b* calorimetric system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a water-based ink set for ink-jetrecording suitable for reducing graininess in a low-density printedpart, for extending a color reproduction range, for improving lightfastness and for improving gas resistance. The present invention alsorelates to an ink-jet recording method using this water-based ink setfor ink-jet recording.

2. Description of the Related Art

When a color image is formed by use of an ink-jet recording method, athree-color ink set has been generally used which is composed of ayellow ink (Y), a magenta ink (M) and a cyan ink (C). Alternatively, afour-color ink set has also been used in which a black ink (K) isfurther added to the three-color ink set.

Generally, in an ink-jet recording method, the gradation of an image iscontrolled by adjusting the density of dots formed by ejecting ink ontoa recording material. However, when the gradation is controlled by sucha method, the dot density decreases in a low-density printed part.Relative to this, the individual dots become easily discernable to theeye, thereby causing a problem that the image is grainy.

In view of the above, a method has been proposed in which two or moreinks are employed as cyan ink (see Japanese Patent Application Laid-OpenNo. H01-95093). In this method, these inks have different dyeconcentrations and are composed of different kinds of dyes. In addition,a dye which is excellent in vividness but inferior in light fastness isemployed in a dark color ink, and a dye which is excellent in lightfastness but inferior in vividness is employed in a light color ink.Moreover, a similar method has been proposed for magenta ink (seeJapanese Patent Application Laid-Open No. H02-127482). According tothese methods, graininess can be improved, but a problem remains that acolor reproduction range cannot be extended. Further, when dye ink isemployed, color fading first occurs in a low-density printed part, andonly the low-density printed part becomes whitish. Thus, the color toneof the image is changed, and the density difference of the image becomesexcessively large to cause the overall image balance to be lost.Therefore, gas resistance, particularly ozone resistance, of a printedpart is important.

Generally, in a three-color ink set composed of yellow, magenta and cyaninks, and also in a four-color ink set in which a black ink is added tothe three-color ink set, red color is developed by use of the magentaink and the yellow ink. When these two inks are used to develop redcolor as above, a problem arises that sharp printing quality and vividcolors are difficult to achieve due to a landing error of superposition.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above-mentionedproblems. Objects of the present invention are, in an ink-jet recordingmethod:

(i) to reduce graininess in a low-density printed part in a magentadirection without reducing the color reproduction range in the magentadirection in a high-density printed part and with minimizing the numberof inks composing an ink set;

(ii) to extend the color reproduction range in a red direction and toenhance vividness;

(iii) to improve light fastness in the magenta and red directions; and

(iv) to improve gas resistance in the magenta and red directions.

The present inventors have conducted extensive studies on a water-basedink set for ink-jet recording. The studies are based on the hypothesisthat the lightness (L*), the hue angle (h) and the chroma (C*) of theinks constituting the ink set are closely related to reducing graininessin a low-density printed part of a color image and to extending a colorreproduction range. Here, the lightness (L*), the hue angle (h) and thechroma (C*) are based on L*a*b* colorimetric system. Consequently, thepresent inventors have found that, in a water-based ink set for ink-jetrecording having a magenta ink, the above-mentioned objects (i), (ii)and (iii) can be achieved by employing a light magenta pigment ink asthe magenta ink and also employing a red ink (e.g., red dye ink). Thislight magenta pigment ink employs pigment as a coloring agent, has alightness (L*) of a specific value or more, and is employed in place ofa normal magenta ink employed in a conventional ink set. Also, the reddye ink employs dye as a coloring agent. Thus, the present invention hasbeen completed.

Accordingly, the present invention provides a water-based ink set forink-jet recording comprising a magenta pigment ink employing pigment asa coloring agent and a red dye ink employing dye as a coloring agent.This ink set is characterized in that the magenta pigment ink is a lightmagenta pigment ink having a lightness (L*) of about 50 or more in theL*a*b* calorimetric system.

In addition, the present invention provides an ink-jet recording methodemploying the above-mentioned water-based ink set for ink-jet recording.

The water-based ink set for ink-jet recording of the present inventioncomprises, as a magenta ink, a light magenta ink which contains a lowconcentration of coloring agent. Therefore, when ink-jet recording isperformed by use of this ink set, the graininess of a low-densityprinted part in a magenta direction can be reduced.

Also, since the coloring agent of the light magenta ink is pigment,excellent light fastness and gas resistance can be obtained in a printedpart in the magenta direction, and color fading and discoloration can beprevented even when the density of magenta color is low.

In addition, this light magenta pigment ink may be ejected on ared-printed part. In this manner, light fastness and gas resistance in ared direction can be improved with little change in the hue of redcolor.

Further, the ink set of the present invention comprises the red dye inktogether with the light magenta pigment ink. Therefore, by employing thered ink together with the light magenta pigment ink in a magenta-printedpart, the color reproduction range in the magenta direction is preventedfrom being reduced in a high-density printed part. In addition, thecolor reproduction range in the red direction is significantly extended,and the vividness of red color is improved. This improvement of thevividness of red color is achieved, since red color is not developed bycolor mixing of a magenta ink and a yellow ink but can be developed bythe red dye ink alone.

Moreover, since the ink employed for developing red color is a dye ink,colors in the range from magenta to red can be reproduced with higherchroma.

In short, according to the ink set of the present invention, thefollowing effects can be attained by use of the two inks including thelight magenta pigment ink and the red dye ink: the reduction ofgraininess in a low-density printed part in the magenta direction; theprevention of the reduction of the color reproduction range in themagenta direction in a high-density printed part; the significantextension of the color reproduction range in the red direction; theimprovement of the vividness of red color; and the improvement of lightfastness and gas resistance in printed parts in the magenta and reddirections.

Therefore, according to the ink set of the present invention, colorreproducibility, print quality, light fastness and gas resistance can beimproved in a color image formed by an ink-jet recording method.

Generally, red color is the second most frequently used color next toblack color upon text printing. According to the present invention,since text in red color is not printed with the superposition of twoinks but can be printed with the single red ink, excellent colordeveloping properties and sharp print quality with suppressed featheringcan be achieved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will next be described in detail.

In the present invention, lightness (L*), hue angle (h) and chroma (C*)are defined based on the L*a*b* colorimetric system standardized by theCommission Internationale de l'Eclairage (CIE) in 1976. Thiscalorimetric system is also defined in Japanese Industrial Standards(JIS Z 8729).

In the present invention, the lightness (L*) is a lightness value in anobject solidly printed at a resolution of 1200×1200 dpi with each of theinks on glossy paper and is obtained by means of a spectrocolorimeter ora similar apparatus. Also, the hue angle (h) and the chroma (C*) are therespective values in the same solidly printed object. In this case,first, color indices (a* and b*) are obtained by means of aspectrocolorimeter or a similar apparatus, and the hue angle (h) and thechroma (C*) are calculated from the following equations (1) and (2)using the obtained a* and b*. $\begin{matrix}{C^{*} = \sqrt{( a^{*} )^{2} + ( b^{*} )^{2}}} & {{Equation}\quad(1)} \\{{h = {{\tan^{- 1}( \frac{b^{*}}{a^{*}} )}( {{{when}\quad a^{*}} \geqq {0\quad{and}{\quad\quad}b^{*}} \geqq 0} )}}{h = {360 + {{\tan^{- 1}( \frac{b^{*}}{a^{*}} )}( {{{when}\quad a^{*}} \geqq {0\quad{and}\quad b^{*}} < 0} )}}}{h = {180 + {{\tan^{- 1}( \frac{b^{*}}{a^{*}} )}( {{{when}{\quad\quad}a^{*}} < 0} )}}}} & {{Equation}\quad(2)}\end{matrix}$

The “glossy paper” employed in the measurement of the L*, a* and b*values is paper having a coat layer for surface smoothness provided onbase paper (body paper). Specific examples of the glossy paper includeKASSAI (a registered trade mark) glossy finishing (product of FUJI PhotoFilm Co., Ltd.), ink-jet printer paper (glossy paper, product of KOKUYOCo., Ltd.), thick glossy paper (product of Kodak Co., Ltd.) and thelike. The term “object solidly printed at a resolution of 1200×1200 dpi”refers to an area which is printed at a resolution of 1200×1200 dpi soas to be fully covered with ink. An ink-jet printer is employed forprinting, and examples of the ink-jet printer include a digitalmultifunction device equipped with an ink-jet printer (MFC-5200J,product of Brother Industries, Ltd.) and the like. Examples of thespectrocolorimeter which can be used include Spectrolino (product ofGretag Macbeth) and the like. The measurement is performed by use of alight source D₆₅ at a viewing angle of 2°.

The water-based ink set for ink-jet recording of the present inventioncomprises a magenta pigment ink and a red dye ink, and is characterizedin that the magenta pigment ink is a light magenta pigment ink having alightness (L*) of 50 or more. Therefore, a normal magenta ink having alightness (L*) of less than 50 is not included in the ink set of thepresent invention. If this normal magenta ink having a lightness (L*) ofless than 50 is employed as the magenta ink, graininess is noticeable ina low-density printed part in the magenta direction. Thus, this normalmagenta ink is not preferable as the magenta ink.

Preferably, the light magenta pigment ink constituting the ink set ofthe present invention has a lightness (L*) of about 50 or more and about65 or less. The light magenta pigment ink having a lightness (L*)exceeding about 65 is not preferable, since the original magenta coloris difficult to reproduce.

Preferably, the hue angle (h) of the light magenta pigment ink isadjusted within the ranges of from about 335° to about 360° or fromabout 0° to about 5°. If the hue angle (h) is not within this range,magenta color is not satisfactorily developed.

Further, preferably, the chroma (C*) of the light magenta pigment ink isadjusted within the range of from about 65 to about 90. By adjusting thechroma (C*) within this range, magenta color can be reproduced vividly.

Preferably, the red dye ink constituting the ink set of the presentinvention has a lightness (L*) of about 50 or less. The red dye inkhaving a lightness (L*) exceeding about 50 is not preferable, since itis difficult to obtain a sufficient color reproduction range in the reddirection. More preferably, the lightness (L*) of the red dye ink fallswithin the range of from about 25 to about 50. By adjusting thelightness (L*) of the red dye ink within this range, red and magentacolors can be reproduced at a satisfactory density.

Preferably, the hue angle (h) of the red dye ink is adjusted within therange of from about 20° to about 35°. By adjusting the hue angle (h)within this range, red color can be satisfactorily developed.

Further, preferably, the chroma (C*) of the red dye ink is adjustedwithin the range of from about 80 to about 90. By adjusting the chroma(C*) within this range, vivid red color can be developed.

Further, the ink set of the present invention may include any ink inaddition to the light magenta pigment ink and the red dye ink. Forexample, a yellow ink and/or a cyan ink may be included in the ink set.A black ink may be included in accordance with need. A full color imagecan be reproduced by including the yellow ink, the cyan ink, and, ifnecessary, the black ink in addition to the light magenta pigment inkand the red dye ink.

If the cyan ink is included in the ink set of the present invention, anormal cyan ink employed in a known ink set may be employed as the cyanink. However, preferably, a light cyan ink having a lightness (L*) ofabout 60 or more is employed in place of the normal cyan ink, and a blueink and/or a green ink are/is also employed. In this case, a normal cyanink having a lightness (L*) of less than about 60 is unnecessary. Byemploying the light cyan ink having a lightness (L*) of about 60 or moreas the cyan ink, graininess can be reduced in a low-density printed partin the cyan direction. Preferably, the lightness (L*) of the light cyanink falls within the range of from about 60 to about 85. The light cyanink having a lightness (L*) exceeding about 85 is not preferable, sincethe original cyan color is difficult to reproduce.

Preferably, the hue angle (h) of the light cyan ink is adjusted withinthe range of from about 215° to about 255°. If the hue angle (h) is notset in this range, it is difficult to satisfactorily develop cyan color.

Further, preferably, the chroma (C*) of the light cyan ink is adjustedwithin the range of from about 40 to about 70. By adjusting the chroma(C*) within this range, cyan color can be reproduced vividly.

Preferably, the blue ink constituting the ink set of the presentinvention together with the light cyan ink has a lightness (L*) of about45 or less. If the lightness (L*) of the blue ink exceeds about 45, itis difficult to obtain a sufficient color reproduction range in the bluedirection. More preferably, the lightness (L*) of the blue ink fallswithin the range of from about 35 to about 45. By adjusting thelightness (L*) of the blue ink within this range, blue and cyan colorscan be reproduced at a satisfactory density.

Preferably, the hue angle (h) of the blue ink is adjusted within therange of from about 270° to about 285°. By adjusting the hue angle (h)within this range, blue color can be satisfactorily developed.

Further, preferably, the chroma (C*) of the blue ink is adjusted withinthe range of from about 70 to about 80. By adjusting the chroma (C*)within this range, blue color can be reproduced vividly.

Preferably, the green ink constituting the ink set of the presentinvention together with the light cyan ink has a lightness (L*) of about60 or less. If the lightness (L*) of the green ink exceeds about 60, itis difficult to obtain a sufficient color reproduction range in thegreen direction. More preferably, the lightness (L*) of the green inkfalls within the range of from about 35 to about 60. By adjusting thelightness (L*) of the green ink within this range, green and cyan colorscan be reproduced at a satisfactory density.

Preferably, the hue angle (h) of the green ink is adjusted within therange of from about 175° to about 215°. By adjusting the hue angle (h)within this range, green color can be satisfactorily developed.

Further, preferably, the chroma (C*) of the green ink is adjusted withinthe range of from about 60 to about 80. By adjusting the chroma (C*)within this range, green color can be reproduced vividly.

Furthermore, at least one of the coloring agents of the light cyan inkand the blue ink and/or the green ink may be employed a pigment.

If a yellow ink or a black ink is included in the ink set of the presentinvention, an ink employed in a known ink set may be employed as theseinks. For example, a normal yellow ink having the hue angle (h) of fromabout 70° to about 140° may be employed as the yellow ink.

Each of the inks constituting the ink set of the present inventioncontains a coloring agent, water and a water soluble organic solvent soas to have L*, h and C* of the predetermined values described above.

Water soluble dye or pigment may be employed as the coloring agentcontained in the inks. A proper combination of these may be employed toadjust the inks to have the predetermined color.

Typical examples of the water soluble dye employed include direct dyes,acid dyes, basic dyes, reactive dyes and the like. Also, examples of thepreferable water soluble dye include, in view of a chemical structure,azo dyes, metal complex dyes, naphthol dyes, anthraquinone dyes, indigodyes, carbonium dyes, quinoneimine dyes, xanthene dyes, aniline dyes,quinoline dyes, nitro dyes, nitroso dyes, benzoquinone dyes,naphthoquinone dyes, phthalocyanine dyes, metal phthalocyanine dyes andthe like. Particularly, examples of the water soluble dye which issuitable as the ink for an ink-jet recording method and satisfies therequired properties such as vividness, water solubility, stability andlight fastness include, but are not limited to: direct dyes such as C.I. Direct Yellows 12, 24, 26, 27, 28, 33, 39, 58, 86, 98, 100, 132 and142, C. I. Direct Reds 4, 17, 28, 37, 63, 75, 79, 80, 81, 83 and 254, C.I. Direct Violets 47, 48, 51, 90 and 94, C. I. Direct Blues 1, 6, 8, 15,22, 25, 71, 76, 80, 86, 87, 90, 106, 108, 123, 163, 165, 199 and 226, C.I. Direct Greens 1, 26, 28, 59, 80 and 85, and the like; acid dyes suchas C. I. Acid Yellows 3, 11, 17, 19, 23, 25, 29, 38, 42, 49, 59, 61, 71and 72, C. I. Acid Reds 1, 6, 8, 18, 32, 35, 37, 42, 52, 85, 88, 115,133, 134, 154, 186, 249, 289 and 407, C. I. Acid Violets 10, 34, 49 and75, C. I. Acid Blues 9, 22, 29, 40, 59, 62, 93, 102, 104, 112, 113, 117,120, 167, 175, 183, 229 and 234, C. I. Acid Greens 3, 5, 9, 12, 15, 16,19, 25, 27, 28, 36, 40, 41, 43, 44, 56, 73, 81, 84, 104, 108 and 109,and the like; basic dyes such as C. I. Basic Yellow 40, C. I. Basic Reds9, 12 and 13, C. I. Basic Violets 7, 14, and 27, C. I. Basic Blues 1, 3,5, 7, 9, 24, 25, 26, 28 and 29, C. I. Basic Greens 1 and 4, and thelike; and reactive dyes such as C. I. Reactive Yellow 2, C. I. ReactiveReds 4, 23, 24, 31 and 56, C. I. Reactive Blues 7, 13 and 49, C. I.Reactive Greens 5, 6, 7, 8, 12, 15, 19 and 21, and the like.

In addition, examples of the pigment include, but are not limited to, C.I. Pigment Yellows 1, 2, 3, 13, 16, 74, 83, 93, 128, 134 and 144, C. I.Pigment Reds 5, 7, 12, 23, 48 (Mn), 57 (Ca), 112, 122, 144, 170, 177,221, 254 and 264, C. I. Pigment Violets 19, 23 and 48 (Ca), C. I.Pigment Blues 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:4, 15:5, 15:6, 16, 17:1,22, 27, 28, 29, 36 and 60, C. I. Pigment Green 7, and the like.

Water soluble dye or pigment may be employed as the coloring agent ofthe black ink, and a proper combination thereof may also be employed.Examples of the water soluble dye include, but are not limited to:direct dyes such as C. I. Direct Blacks 17, 19, 32, 51, 71, 108, 146,154 and 168, and the like; acid dyes such as C. I. Acid Blacks 2, 7, 24,26, 31, 52, 63, 112 and 118, and the like; basic dyes such as C. I.Basic Black 2, and the like; C. I. Food Blacks 1 and 2, and the like.Examples of the pigment which can be employed include carbon blacks suchas MA8, MA100 (products of Mitsubishi Chemical Corporation), and colorblack FW200 (product of Degussa). A self-dispersing type carbon blackwhich can disperse in water without using a dispersing agent may beemployed as the carbon black. A self-dispersing type carbon black can beobtained by subjecting a carbon black to a surface treatment such thatat least one hydrophilic group such as a carbonyl group, a carboxylgroup, a hydroxyl group, or a sulfone group or a salt thereof is boundto the surface of the carbon black. Specific examples of the surfacetreatment include a method disclosed in U.S. Pat. No. 5,609,671 and amethod disclosed in WO97/48769. Alternatively, a commercial product suchas CAB-O-JET (a registered trade mark) 200, 300 (products of CabotCorporation) or BONJET (a registered trade mark) CW1 (product of OrientChemical Industries, Ltd.) may be employed as the self-dispersing blackpigment.

The amount of the water soluble dye contained in the dye ink depends onthe desired printing density and the desired color. If the amount is toolow, the color is not satisfactorily developed on a recording material.On the other hand, if the amount is too high, a nozzle of an ink-jethead tends to be clogged. Thus, the amount of the water soluble dye withrespect to the total weight of the corresponding ink is preferably about0.1 wt. % to about 15 wt. %, more preferably about 0.3 wt. % to about 10wt. %, and particularly preferably about 0.5 wt. % to about 5.0 wt. %.

The amount of the pigment contained in the pigment inks depends on thedesired printing density and the desired color. If the amount is toolow, the color is not satisfactorily developed on a recording material.On the other hand, if the amount is too high, a nozzle of an ink-jethead tends to be clogged. Thus, the amount of the pigment with respectto the total weight of the corresponding ink is preferably about 0.2 wt.% to about 15 wt. %, and more preferably about 0.2 wt. % to about 10 wt.%.

Preferably, the water employed in the inks is deionized water. Theamount of the water is determined based on the kind of the water solubleorganic solvent, the composition of the ink and the desired inkproperties. If the amount of the water is too low, the viscosity of theink increases to cause difficulty in ejecting the ink from a nozzle ofan ink-jet head. On the other hand, if the amount is too high, thecoloring agent is precipitated or aggregated due to the evaporation ofwater, and thus a nozzle of an ink-jet head tends to be clogged.Therefore, the amount of the water with respect to the total weight ofthe corresponding ink is preferably about 10 wt. % to about 95 wt. %,more preferably about 10 wt. % to about 90 wt. %, and particularlypreferably about 20 wt. % to about 80 wt. %.

The water soluble organic solvents employed in the inks are broadlycategorized into a humectant and a penetrant.

The humectant is added to the ink for preventing clogging of a nozzle ofan ink-jet head. Specific examples of the humectant include, but are notlimited to, water soluble glycols such as glycerin, ethylene glycol,diethylene glycol, triethylene glycol, polyethylene glycol, propyleneglycol, dipropylene glycol, tripropylene glycol, polypropylene glycol,1,5-pentanediol, 1,6-hexanediol and the like. If the amount of the watersoluble organic solvent serving as the humectant is too low, theclogging of a nozzle of an ink-jet head is not satisfactorily prevented.On the other hand, if the amount is too high, the viscosity of the inkincreases to cause difficulty in ejecting. Therefore, the amount of thewater soluble organic solvent with respect to the total weight of thecorresponding ink is preferably about 5 wt. % to about 50 wt. %, morepreferably about 5 wt. % to about 40 wt. %, and particularly preferablyabout 5 wt. % to about 35 wt. %.

The penetrant is added to the ink for allowing the ink to rapidlypenetrate into paper upon printing. Specific examples of the penetrantinclude glycol ethers typified by ethylene glycol-based alkyl ethers,propylene glycol-based alkyl ethers and the like. Specific examples ofthe ethylene glycol-based alkyl ether include, but are not limited to,ethylene glycol methyl ether, ethylene glycol ethyl ether, ethyleneglycol-n-propyl ether, ethylene glycol-n-butyl ether, ethylene glycolisobutyl ether, diethylene glycol methyl ether, diethylene glycol ethylether, diethylene glycol-n-propyl ether, diethylene glycol-n-butylether, diethylene glycol isobutyl ether, triethylene glycol methylether, triethylene glycol ethyl ether, triethylene glycol-n-propylether, triethylene glycol-n-butyl ether, triethylene glycol isobutylether and the like. Specific examples of the propylene glycol-basedalkyl ether include, but are not limited to, propylene glycol methylether, propylene glycol ethyl ether, propylene glycol-n-propyl ether,propylene glycol-n-butyl ether, dipropylene glycol methyl ether,dipropylene glycol ethyl ether, dipropylene glycol-n-propyl ether,dipropylene glycol-n-butyl ether, tripropylene glycol methyl ether,tripropylene glycol-n-ethyl ether, tripropylene glycol-n-propyl ether,tripropylene glycol-n-butyl ether and the like.

If the amount of the water soluble organic solvent serving as thepenetrant is too low, the penetrability is unsatisfactory. On the otherhand, if the amount is too high, the penetrability becomes excessivelyhigh, and thus blurring such as feathering tends to occur. Therefore,the amount of the water soluble organic solvent with respect to thetotal weight of the corresponding ink is preferably about 0.1 wt. % toabout 10 wt. %, and more preferably about 0.1 wt. % to about 5 wt. %.

In addition to the above-described humectant and penetrant, the inksconstituting the ink set of the present invention may contain a watersoluble organic solvent to prevent drying of ink at the tip of anink-jet head, to enhance printing density, and to help the developmentof vivid colors. Examples of such a water soluble organic solventinclude, but are not limited to: lower alcohols such as methyl alcohol,ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol,sec-butyl alcohol, tert-butyl alcohol and the like; amides such asdimethylformamide, dimethylacetamide and the like; ketones andketo-alcohols such as acetone, diacetone alcohol and the like; etherssuch as tetrahydrofuran, dioxane and the like; glycerin; 2-pyrrolidone;N-methyl-2-pyrrolidone; 1,3-dimethyl-2-imidazolidinone; and the like.

Moreover, other conventionally known surfactants; viscosity modifierssuch as polyvinyl alcohol, cellulose, water soluble resin and the like;surface tension modifiers; mildewproofing agents; or the like may beadded to the inks constituting the ink set of the present invention inaccordance with need.

The ink-jet recording method of the present invention performs ink-jetrecording by use of the ink set of the present invention. No particularlimitation is imposed on the type of the ink-jet recording method.Examples of the ink-jet recording method include, but are not limitedto, an electrostatic attraction method, a method using a piezoelectricelement, and a thermal method.

In the ink-jet recording method of the present invention, the lightmagenta pigment ink may be employed on a recording part in a recordingmaterial together with the red dye ink. In this case, the use ratio ofthe light magenta pigment ink to the red dye ink (i.e., the volumepercentage of the light magenta pigment ink with respect to the red dyeink) is preferably about 25% or more and about 75% or less. A use ratioof the light magenta pigment ink of less than about 25% is notpreferable, since an improving effect on light fastness of red color islow. In addition, a use ratio of the light magenta pigment ink ofexceeding about 75% is not preferable, since the tone of red color isevidently changed. Of course, for colors which can be developed by thelight magenta pigment ink alone, the red dye ink may not be employedtogether therewith.

In the ink-jet recording method of the present invention, when the lightmagenta pigment ink is employed on a recording material together withthe red dye ink, the landing order of the inks is not particularlylimited so long as the tone of the desired color can be reproduced.However, if the light magenta pigment ink is allowed to land in asuperposing manner on a part recorded with the red dye ink, the lightfastness is improved. This is because the amount of light reaching thedye molecules present in the lower layer decreases, since the pigment ispresent on the surface of the printed object. For a similar reason, theamount of oxides such as ozone which attack the dye molecules present inthe lower layer decreases, thereby improving the gas resistance. On theother hand, if the red dye ink is allowed to land in a superposingmanner on a part in a recording material on which part the light magentapigment ink lands in advance, the color developing properties areimproved by the light transparency of the dye molecules.

EXAMPLES

The present invention will next be specifically described by way ofExamples and Comparative Examples. In the present Examples, “%” refersto weight % unless otherwise specified.

Examples 1 to 5 and Comparative Examples 1 to 7

(1) Preparation of Pigment Inks

Light magenta pigment ink 1 was prepared as follows.

First, 15 parts by weight of C. I. Pigment Red 122, 5 parts by weight ofpolyoxyethylene lauryl ether ammonium sulfate (average polymerizationdegree of oxyethylene=12), 15 parts by weight of glycerin and 65 partsby weight of water (ion exchanged water) were mixed. Subsequently, themixture was subjected to a dispersion treatment by means of a wet sandmill using zirconia beads having a diameter of 0.3 mm as a medium tothereby obtain 100 parts by weight of a magenta pigment dispersion.

Separately, 52.3 parts by weight of water (ion exchanged water), 23.7parts by weight of glycerin and 2 parts by weight of dipropyleneglycol-n-propyl ether (hereinafter referred to as DPGPE) were mixed toprepare 78 parts by weight of an ink solvent. Subsequently, 22 parts byweight of the above-described magenta pigment dispersion was weighed outfrom 100 parts by weight thereof, and 78 parts by weight of the preparedink solvent was gradually added thereto under stirring. The mixture wascontinued to stir for 30 minutes and filtrated with a membrane filterhaving a pore size of 1 μm to prepare light magenta pigment ink 1. Theblending amount of C. I. Pigment Red 122 with respect to the totalweight of the ink was 3.3 wt. %.

The same procedure as in the case of light magenta pigment ink 1 wasrepeated except that the ink composition was changed as shown in Table 1to prepare light magenta pigment inks 2 and 3, and a normal magentapigment ink.

(2) Preparation of Dye Inks

Red dye ink 1 was prepared as follows.

First, 68.5 parts by weight of water, 27 parts by weight of glycerin and2 parts by weight of DPGPE were mixed to prepare 97.5 parts by weight ofan ink solvent. Subsequently, 2.5 parts by weight of a red water solubledye (C. I. Direct Red 254) was added to 97.5 parts by weight of the inksolvent under stirring. The mixture was continued to stir for 30 minutesand filtrated with a membrane filter having a pore size of 1 μm toprepare red dye ink 1.

The same procedure as in the case of red dye ink 1 was repeated exceptthat the ink composition was changed as shown in Table 1 to prepare ared dye ink 2, a normal magenta dye ink, light magenta dye inks 1 and 2and a yellow ink.

(3) Determination of L*, a*, b*, C* and h

Each of the inks was filled into a predetermined ink cartridge, and theink cartridge was attached to a digital multifunction device equippedwith an ink-jet printer (MFC-5200J, product of Brother Industries,Ltd.). Subsequently, an object was solidly printed with the ink at aresolution of 1,200×1,200 dpi on glossy paper (KASSAI (a registeredtrade mark) glossy finishing, product of FUJI Photo Film Co., Ltd.). Thesolidly printed object was measured for L*, a* and b* by means ofSpectrolino (product of Gretag Macbeth) (light source: D₆₅, viewingangle: 2°).

The values of C* and h were calculated according to the followingequations (1) and (2) using the obtained measurement values. The resultsare shown in Table 1. $\begin{matrix}{C^{*} = \sqrt{( a^{*} )^{2} + ( b^{*} )^{2}}} & {{Equation}\quad(1)} \\{{h = {{\tan^{- 1}( \frac{b^{*}}{a^{*}} )}( {{{when}\quad a^{*}} \geqq {0\quad{and}{\quad\quad}b^{*}} \geqq 0} )}}{h = {360 + {{\tan^{- 1}( \frac{b^{*}}{a^{*}} )}( {{{when}\quad a^{*}} \geqq {0\quad{and}\quad b^{*}} < 0} )}}}{h = {180 + {{\tan^{- 1}( \frac{b^{*}}{a^{*}} )}( {{{when}{\quad\quad}a^{*}} < 0} )}}}} & {{Equation}\quad(2)}\end{matrix}$(4) Configuration of Ink Sets

The inks shown in Table 1 were combined as shown in Table 2 to configurewater-based ink sets for ink-jet recording. Comparative Example 5corresponds to a conventional ink set.

(5) Evaluation of Ink Sets

For each of the ink sets shown in Table 2, the inks constituting the inkset were filled into predetermined ink cartridges, and the inkcartridges were attached to a digital multifunction device equipped withan ink-jet printer (MFC-5200J, product of Brother Industries, Ltd.).Subsequently, a gradation sample and a print pattern sample were printedon glossy paper (KASSAI (a registered trade mark) glossy finishing,product of FUJI Photo Film Co., Ltd.). The gradation sample was employedfor graininess, light fastness and gas resistance evaluations of magentacolor and was printed for each of the magenta inks (the light magentapigment ink, the light magenta dye ink, the normal magenta pigment inkand the normal magenta dye ink). The print pattern sample was employedfor color reproducibility evaluation of red and magenta colors. Also,this print pattern sample contained patches having various hues whichwere obtained by changing the mixing ratio of the yellow ink, the reddye ink and the magenta ink (the light magenta pigment ink, the lightmagenta dye ink, the normal magenta pigment ink or the normal magentadye ink).

The patches of each of the obtained samples were measured for a*, b* andL* by means of the same method as above. Subsequently, (a) graininessevaluation of magenta color, (b) evaluation of red colorreproducibility, (c) evaluation of magenta color reproducibility, (d)evaluation of light fastness of a magenta color-printed part, (e)evaluation of gas resistance of a magenta color-printed part and (f)overall evaluation were performed for each of the ink sets as follows.

(a) Graininess Evaluation of Magenta Color

The patch for L*=90 in the above gradation sample was visually observed,and the graininess of magenta color was evaluated according to thefollowing criteria. The evaluation results are shown in Table 2.

A: Graininess is not found.

B: Graininess is hardly noticeable.

C: Graininess is noticeable. Practically problematic.

(b) Evaluation of Red Color Reproducibility

(b-1) Visual Evaluation

A patch having a hue angle (h) of 33°±10° was selected from theabove-mentioned print pattern sample. Here, the above hue angle (h)corresponds to red color. The selected red color patch was visuallyobserved to evaluate, based on the following criteria, whether or notthe red color was satisfactorily developed. The evaluation results areshown in Table 2.

A: High-density red color is satisfactorily developed.

B: High-density red color is developed.

C: High-density red color is not satisfactorily developed.

(b-2) Chroma (C*) and lightness difference (ΔL*)

A patch having a hue angle (h) of 33°±10° was selected from the aboveprint pattern sample. Here, the color having the above hue angle (h) iscategorized as red color. The selection was made such that the selectedpatch had a hue angle (h) closest to that of the patch showing the redcolor printed by use of a conventional ink set; i.e., the patch ofComparative Example 5 (h=33°, L*=50). Subsequently, the chroma (C*) wascalculated according to equation (1) above for each selected patch.

The lightness difference (ΔL*) between each selected patch and the patchof Comparative Example 5 was calculated according to the followingequation (3). The larger value of the lightness difference (ΔL*)represents that high-density red color is less satisfactorily developed.ΔL*=L* ₂ −L* ₁  Equation (3)L*₁: L* of Comparative Example 5L*₂: L* of Examples and Comparative Examples(c) Evaluation of Magenta Color Reproducibility(c-1) Visual Evaluation

A patch having a hue angle (h) of 359°±10° was selected from theabove-mentioned print pattern sample. Here, the above hue angle (h)corresponds to magenta color. The selected magenta color patch wasvisually observed to evaluate, based on the following criteria, whetheror not the magenta color was satisfactorily developed. The evaluationresults are shown in Table 2.

A: High-density magenta color is satisfactorily developed.

B: Color close to high-density magenta color is developed.

C: High-density magenta color is not satisfactorily developed.

(c-2) Chroma (C*) and Lightness Difference (ΔL*)

A patch having a hue angle (h) of 359°±10° was selected from the aboveprint pattern sample. Here, the color having the above hue angle (h) iscategorized as magenta color. The selection was made such that theselected patch had a hue angle (h) closest to that of the patch showingthe magenta color printed by use of the conventional ink set; i.e., thepatch of Comparative Example 5 (h=359°, L*=49). Subsequently, the chroma(C*) was calculated according to equation (1) above for each selectedpatch. Further, the lightness difference (ΔL*) between each selectedpatch and the patch of Comparative Example 5 was calculated according tothe above equation (3). The larger value of the lightness difference(ΔL*) represents that high-density magenta color is less satisfactorilydeveloped.

(d) Evaluation of Light Fastness of a Magenta Color-Printed Part

A light fastness test was performed by use of the above gradation sampleas follows.

The light fastness test was performed by means of a high energy xenonweather meter (SC750-WN, product of Suga Test Instruments Co., Ltd.). Inthis case, a xenon lamp was employed as a light source, and the test wasperformed under the conditions of a temperature of 25° C., a humidity of50% RH, an irradiance of 35 W/m² (300 to 400 nm) and an irradiation timeof 100 hours.

For a gradation sample having an OD value of 0.6 before the lightfastness test, the OD value after the light fastness test was obtained.The OD values were obtained by use of the reflection densitometer RD-914(product of Gretag Macbeth). An OD value reduction ratio with respect tothe OD value (0.6) of the patch before the test was obtained from thefollowing equation (4), and the obtained OD value reduction ratio wasevaluated according to the following criteria. The evaluation resultsare shown in Table 2. $\begin{matrix}{{{OD}{\quad\quad}{value}{\quad\quad}{reduction}{\quad\quad}{ratio}\quad(\%)} = {\frac{{OD}_{b} - {OD}_{a}}{{OD}_{b}} \times 100}} & {{Equation}\quad(4)}\end{matrix}$OD_(b): OD value before test (=0.6)OD_(a): OD value after test

A: The OD value reduction ratio is less than 30%.

B: The OD value reduction ratio is 30% or more.

(e) Evaluation of Gas Resistance of a Magenta Color-Printed Part

An ozone resistance test as gas resistance evaluation was performed byuse of the above gradation sample.

The ozone resistance test was performed by allowing a sample to standunder an atmosphere of an ozone concentration of 1 ppm, a chambertemperature of 24° C. and a humidity of 60% RH for 200 hours by use ofthe Ozone Weather Meter OMS-H (product of Suga Test Instruments Co.,Ltd.).

For a gradation sample having an OD value of 0.6 before the ozoneresistance test, the OD value after the ozone resistance test wasmeasured by the same method as in the light fastness test. An OD valuereduction ratio with respect to the OD value (0.6) of the patch beforethe test was obtained from the foregoing equation (4), and the obtainedOD value reduction ratio was evaluated according to the followingcriteria. The evaluation results are shown in Table 2.

A: The OD value reduction ratio is less than 30%.

B: The OD value reduction ratio is 30% or more.

(f) Overall Evaluation

Overall evaluation was conducted based on the evaluation results of theink set according to the following criteria. The results are shown inTable 2.

A: All of the evaluation results are rank A or rank B.

B: The evaluation results for the graininess evaluation of magentacolor, the evaluation of red color reproducibility and the evaluation ofmagenta color reproducibility are rank A or rank B.

C: The evaluation results for the graininess evaluation of magentacolor, the evaluation of red color reproducibility and the evaluation ofmagenta color reproducibility contain rank C. TABLE 1 Light Light LightNormal Light Light Red Red magenta magenta magenta magenta magentamagenta Normal dye dye pigment pigment pigment pigment dye ink dye inkmagenta ink ink Yellow ink 1 ink 2 ink 3 ink 1 2 dye ink 1 2 ink InkC.I. Pigment Red 3.3 2.5 1.7 5.0 — — — — — — Compo- 122 sition C.I. AcidRed 52 — — — — 1.6 1.3 2.5 — — — (wt. %) C.I. Direct Red 254 — — — — — —— 2.5 — — C.I. Direct Red 81 — — — — — — — — 2.5 — C.I. Direct Yellow —— — — — — — — — 0.4 86 C.I. Direct Yellow — — — — — — — — — 1.6 132Glycerin 27.0 27.0 27.0 27.0 27.0 27.0 27.0 27.0 27.0 27.0 Dipropyleneglycol- 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 n-propyl etherPolyoxyethylene 1.1 0.8 0.6 1.7 — — — — — — lauryl ether ammoniumsulfate (*1) Water 66.6 67.7 68.7 64.3 69.4 69.7 68.5 68.5 68.8 69.0Colori- L* 51 55 65 46 51 54 49 32 41 — metric C* 80 75 68 76 84 83 8580 89 — system h/° 352 348 346 355 355 351 359 33 32 —(*1) Average polymerization degree of oxyethylene = 12*The ink composition (wt. %) represents the actual blending ratio ofeach ink component with respect to the total weight of an ink.

TABLE 2 Comp. Comp. Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex.4 Ex. 5 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ink Magenta ink LightLight Light Light Light Light Normal Normal Light Normal Normal Lightmagenta magenta magenta magenta magenta magenta magenta magenta magentamagenta magenta magenta pigment pigment pigment pigment pigment dye inkpigment pigment pigment dye ink dye ink dye ink ink 1 ink 2 ink 1 ink 2ink 3 1 ink ink ink 2 2 Red ink Red dye Red dye Red dye Red dye Red dyeRed dye — Red dye — — Red dye — ink 1 ink 1 ink 2 ink 2 ink 2 ink 1 ink1 ink 1 Yellow ink Yellow Yellow Yellow Yellow Yellow Yellow YellowYellow Yellow Yellow Yellow Yellow ink ink ink ink ink ink ink ink inkink ink ink Evalu- Graininess of B B B B A B C C B C C B ation magentacolor Red Visual A A A A A A B A C B A C color evaluation repro- L* 3232 41 41 41 32 53 32 60 50 32 56 duci- C* 80 80 89 89 89 80 63 80 57 9280 82 bility h/° 33 33 32 32 32 33 35 33 32 33 33 32 Lightness −18 −18−9 −9 −9 −18 −9 −18 3 Compar- −18 +6 difference ison (ΔL*) refer- enceMagenta Visual A A A A B A A A C A A C color evaluation repro- L* 42 4546 48 49 44 46 46 55 49 49 55 duci- C* 81 75 82 79 78 82 76 76 75 85 8584 bility h/° 1 4 359 3 6 5 355 355 4 359 359 350 Lightness −7 −4 −3 −1±0 −5 −3 −3 +6 Compar- ±0 +6 difference ison (ΔL*) refer- ence Lightfastness A A A A A B A A A B B B of magenta color-printed part Gasresistance A A A A A B A A A B B B of magenta color-printed part Overallevaluation A A A A A B C C C C C C

As shown in Table 2, in each of Examples 1 to 5, the graininess was notfound or was hardly noticeable in a low-density printed part (L*=90) ofmagenta color, since the light magenta ink having a lightness (L*) ofabout 50 or more was employed. Also, since the red ink having alightness (L*) of about 50 or less was employed, high-density red colorwas satisfactorily developed. In these Examples, although the lightmagenta ink having a low lightness (L*) of about 50 or more wasemployed, the red ink was also employed. Therefore, high-density magentacolor could also be developed which was comparable to the magenta colorwhich may be developed by a conventional ink set (Comparative Example5). Further, since the coloring agent of the light magenta ink waspigment, the light fastness and the gas resistance were excellent in amagenta color-printed part.

Moreover, in each of Examples 1 to 5, red color can be developed by thered ink alone. Therefore, a landing error due to superposition was notgenerated in text printed in red color, thereby obtaining sharp printingquality.

In Comparative Example 1, the graininess was hardly noticeable in alow-density printed part (L*=90) of magenta color because the lightmagenta ink having a lightness (L*) of about 50 or more was employed.Also, since the red ink having a lightness (L*) of about 50 or less wasemployed, high-density red color was satisfactorily developed. In thiscase, although the light magenta ink having a low lightness (L*) ofabout 50 or more was employed, the red ink was also employed. Therefore,high-density magenta color could also be developed which was comparableto the magenta color which may be developed by the conventional ink set(Comparative Example 5). However, since the coloring agent of the lightmagenta ink was dye, the light fastness and the gas resistance wereunsatisfactory in a magenta color-printed part.

In Comparative Example 2, since the normal magenta ink having alightness (L*) of less than about 50 was employed, magenta color couldbe developed as comparable to that in the conventional ink set(Comparative Example 5). Also, since the coloring agent of the normalmagenta ink was pigment, the light fastness and the gas resistance wereimproved in a magenta color-printed part. However, since the magenta inkwas the normal magenta ink having a lightness (L*) of less than about50, the graininess was noticeable in a low-density printed part ofmagenta color. In addition, since the red ink was not employed, thecolor reproduction range of red color was inferior to those of the inksets of the present invention (Examples 1 to 5).

In Comparative Example 3, since the normal magenta ink having alightness (L*) of less than about 50 was employed, magenta color couldbe developed as comparable to that in the conventional ink set(Comparative Example 5). Also, since the coloring agent of the normalmagenta ink was pigment, the light fastness and the gas resistance wereimproved in a magenta color-printed part. Further, since the red inkhaving a lightness (L*) of about 50 or less was employed, high-densityred color could be satisfactorily developed. However, since the magentaink was the normal magenta ink having a lightness (L*) of less than 50,the graininess was noticeable in a low-density printed part of magentacolor.

In Comparative Example 4, since the light magenta ink having a lightness(L*) of about 50 or more was employed, the graininess was unnoticeablein a low-density printed part (L*=90) of magenta color. Also, since thecoloring agent of the light magenta ink was pigment, the light fastnessand the gas resistance were improved in a magenta color-printed part.However, since the red ink was not employed, high-density red color wasevidently insufficiently developed. In addition, since the red ink wasnot employed and also since the magenta ink was the light magenta inkhaving a lightness (L*) of about 50 or more, high-density magenta colorwas unsatisfactorily developed. Thus, the ink set of Comparative Example4 was practically problematic.

Comparative Example 5 corresponds to the conventional ink set. Since thenormal magenta ink having a lightness (L*) of less than about 50 wasemployed, the graininess was noticeable in a low-density printed part ofmagenta color. Also, since the coloring agent of the normal magenta inkwas dye, the light fastness and the gas resistance were poor in amagenta color-printed part. Further, since the red ink was not employed,the color reproduction range of red color was inferior to those of theink sets of the present invention (Examples 1 to 5).

In Comparative Example 6, since the normal magenta ink having alightness (L*) of less than about 50 was employed, magenta color couldbe developed as comparable to that in the conventional ink set(Comparative Example 5). Also, since the red ink was employed inaddition to the normal magenta ink, the color reproduction range of redcolor was larger than that of the conventional ink set (ComparativeExample 5). However, since the magenta ink was the normal magenta inkhaving a lightness (L*) of less than 50, the graininess was noticeablein a low-density printed part of magenta color. Further, since thecoloring agent of the normal magenta ink was dye, the light fastness andthe gas resistance were poor in a magenta color-printed part.

In Comparative Example 7, the graininess was unnoticeable in alow-density printed part (L*=90) of magenta color because the lightmagenta ink having a lightness (L*) of about 50 or more was employed.However, the coloring agent of the light magenta ink was dye, the lightfastness and the gas resistance were poor in a magenta color-printedpart. Moreover, since the red ink was not employed, the colorreproduction range of red color was narrower than that of theconventional ink set (Comparative Example 5), and the color reproductionrange of high-density red color was unsatisfactory. In addition, sincethe red ink was not employed and also since the magenta ink was thelight magenta ink having a lightness (L*) of about 50 or more,high-density magenta color was unsatisfactorily reproduced.

As described above, the ink sets of Examples 1 to 5 were superior to theink sets of Comparative Examples 1 to 7 in terms of: reducing graininessin a low-density printed part of magenta color without reducing thecolor reproduction range of magenta color; extending the colorreproduction range of red color; and improving the light fastness andgas resistance in a magenta color-printed part.

According to the water-based ink set for ink-jet recording of thepresent invention, the following can be achieved: the reduction ofgraininess in a low-density printed part in the magenta direction; theextension of color reproduction ranges; and the improvement of lightfastness and gas resistance. Therefore, the ink set of the invention isuseful when a color image is reproduced by a printer for ink-jetrecording.

The entire disclosure of the specification, claims and summary ofJapanese Patent Application No. 2005-246881 filed on Aug. 26, 2005 ishereby incorporated by reference.

1. A water-based ink set for ink-jet recording comprising a magentapigment ink employing pigment as a coloring agent and a red dye inkemploying dye as a coloring agent, wherein the magenta pigment ink is alight magenta pigment ink having a lightness (L*) of about 50 or more inthe L*a*b* colorimetric system.
 2. The water-based ink set for ink-jetrecording according to claim 1, wherein a normal magenta ink having alightness (L*) of less than about 50 in the L*a*b* colorimetric systemis not included as the magenta pigment ink.
 3. The water-based ink setfor ink-jet recording according to claim 1, wherein the light magentapigment ink has the lightness (L*) in a range of from about 50 to about65 in the L*a*b* calorimetric system.
 4. The water-based ink set forink-jet recording according to claims 1, wherein the light magentapigment ink has a hue angle (h) in ranges of from about 335° to about360° or of from about 0° to about 5° in the L*a*b* colorimetric system.5. The water-based ink set for ink-jet recording according to claim 1,wherein the light magenta pigment ink has a chroma (C*) in a range offrom about 65 to about 90 in the L*a*b* calorimetric system.
 6. Thewater-based ink set for ink-jet recording according to claim 1, whereinthe red dye ink has a lightness (L*) of about 50 or less in the L*a*b*calorimetric system.
 7. The water-based ink set for ink-jet recordingaccording to claim 1, wherein the red dye ink has a lightness (L*) in arange of from about 25 to about 50 in the L*a*b* calorimetric system. 8.The water-based ink set for ink-jet recording according to claim 1,wherein the red dye ink has a hue angle (h) in a range of from about 200to about 350 in the L*a*b* colorimetric system.
 9. The water-based inkset for ink-jet recording according to claim 1, wherein the red dye inkhas a chroma (C*) in a range of from about 80 to about 90 in the L*a*b*calorimetric system.
 10. The water-based ink set for ink-jet recordingaccording to claim 1, further comprising a yellow ink and/or a cyan ink.11. The water-based ink set for ink-jet recording according to claim 1,further comprising a black ink.
 12. An ink-jet recording methodemploying the water-based ink set for ink-jet recording according toclaim 1.